Matching funds are requested to complete the purchase of a high-frequency pulsed EPR spectrometer, which will expand dramatically the potential power of this ongoing research project on the Molecular Dynamics of Muscle Contraction (AR32961), as well as several other NIH-funded projects at the University of Minnesota. The Bruker E680 electron paramagnetic resonance (EPR) spectrometer, offers two features that are not available in a commercial spectrometer in the entire upper Midwest: (1) a high-field superconducting magnet and the associated high-frequency (94 GHz, "W-band") operation that is 10 times greater than currently available in Minnesota, and (2) pulsed excitation and the associated time-domain detection. With this instrument, commercial EPR instrumentation has undergone a revolution similar to that of NMR in the 80s and 90s, with the advent of higher frequencies and time-domain technology providing dramatic improvements in sensitivity and resolution, resulting in deeper and more direct physical insight into molecular structure, dynamics, and interactions. This has produced an explosion of research opportunities, opening up whole new areas of investigation in site-directed spin-labeling (SDSL). This instrument transforms the entire project funded by the parent grant (AR32961), Molecular Dynamics of Muscle Contraction, which has played a major role in past decades in developing and applying state-of-the-art EPR techniques to muscle proteins and fibers. High-frequency (multifrequency) EPR makes it possible to analyze spin label orientation and dynamics with new precision, permitting rigorous tests of models based on crystal structures. Pulsed EPR offers the opportunity to resolve multiple conformations and accessibilities and to measure spin-spin distances at twice the range (5 nm) that was possible previously, testing models for large-scale movements of actin and myosin. The extra sensitivity available at high frequency permits the study of structural dynamics within a single muscle fiber, establishing a major breakthrough in structure-function analysis of muscle. These same advantages will also transform other NIH funded projects in the same laboratory, justifying co funding. In "Biophysical Studies of Membrane Molecular Dynamics" (GM27906), the extra resolution and sensitivity will provide new insight into the protein dynamics and interactions involved in muscle calcium regulation. In "Protein, Oxidation, Structure, and Function in Aging Muscle" (AG26160), the enhanced sensitivity will permit the exploration of muscle degeneration at the single-cell level. [unreadable] [unreadable] [unreadable]